A monophosphate of magnesium and sodium

The title compound, magnesium sodium phosphate, Mg5Na2(PO4)4, belongs to a group of monophosphates which are constructed from five kinds of coordination polyhedra: two kinds of PO4 tetrahedra are connected by one type of Mg-O octahedra situated at the centres of symmetry; distorted five-coordinated Mg-O polyhedra and another type of distorted Mg-O octahedra are in general positions. Na-O polyhedra occupy the cavities formed by these five types of coordination polyhedra. The density, Dx, of this compound is 3.00 Mg m-3, reflecting the high-pressure synthesis. Similar compounds precipitated at 1 atm. (101.325 kPa) have densities of 2.55-2.82 Mg m-3, corresponding to the lower pressure condition. (orig.)